Corrosion-resisting coating



M Dec. 10, 1929 1 UNITED STATES PATENT orrlcs RALPH J. WIBSHING AND HENRY 3. EMS, OI IIJIEJSROIIIT,v MICHIGAN, ASSIGNOBS v GENERAL MOTORS RESEARCH CORPORATION, 03 DETROIT, MICHIGAN, A 00329- TION OF DELAWARE COBROSIOH-BESI'STING COATING No Drawing.

The invention relates to means for protecting metal surfaces against deterioratlon and more particularly to the rotection of ferrous metal surfaces expose to agencies tending to cause rust, corrosion or tarnishing.

The covering of metal surfaces with coatings which are themselves resistant to atmospheric and other corrosive agencies is generally em loyed for the purpose both of protect- 10 ing the ase material and of providing a surface of pleasing appearance as well as of nontarnishmg properties. Of recent years chromium has been widely recognized as particularl useful for a surface coatin because of 15 its igh resistance to corrosion y ordinary atmosphericjagencies. I

Chromium alone, when applied to surfaces such as those of ferrous metal, does not, however, provide efl'ective protection. of the unao derlyin metal against rust or like deterioration an numerous combinations of chromium with other metals, successively or simultaneously applied, have been proposed in the efiort to combine the desirab e properties of as chromium as a surface finish with adequate protection of the base metal. Our experiments have led to'the discovery that most extraordinar results are secured b the combination wit an outer coating of so c romium of an underlying layer containin tin. The effect is very greatly enhanced i another layer, preferably of copper or nickel or both, be interposed between the chromium and the tin. As an example of the remarkable efi'ects of such a combination of coatings, it has been found that a steel plate coated with successive layers of co per, nickel and chromium, (hitherto regar ed as a highly efiective rust-resistant coating), failed under the salt spra'r test after 120 hours, whereas a plate of stee coated first with a layer of tin of only 0.00004 inch in thickness, followed by layers of nickel or copper and of chromium of substantiall the same thicknesses as in the first mentioned test, showed no signs of failure after 264 hours under the salt spray. y p

The coating of tin may be applied either electrolytically or by any 0t er sultable method, as by dipping the ferrous article in Application filed March 15, 1928. Serial No. 883,034.

markable results in resisting rust have been obtained, for example, by plating chromium,

with or without an intermediate layer of nickel and/or copper, over ordinary terne plate. While the tin and chromium layers,

without additional coatings, give very remarkable protection to the ferrous base, even better results are obtained by. the interposition of one 'or more additional protective metals as copper or nickel. This is especially. desirable when a bright finish is to be secured on the chromium surface, as it is difi'iclilt to plate chromium with a bright surface over tin. Therefore, when the final chromium surface is to be bright, we prefer to interpose between the tin and chromium a layer of one or more metals which may begiven a bright surface upon which bright chromium may be plated. Nickel and/or copper are suitable for this purpose.

Very satisfactory results have. aw: ob-- tained from .coating the ferrous metal base with tin copper and chromium in the order given. owever inasmuch as the copper coating is etched b chromic acid, it is desirable, when a brig t surface finish of chromium is desired and a chromicacid bath is to.

be used, to coat the cop er with a metal resistant tothe corrosive ects of chromic acid and bufi the same before depositing the final coating of chromium. For this reason the coating of nickel over the copper is referred.

If the tin is applied electrolytica ly it may be plated from a bath containing stannous chloride or sodium stannate. The copper may be plated from a co per cyanide bath the nickel from a nicke acetate bath an the chromium from a chromic acid bathu Other baths, however, may be substituted for 1 i.

these as desired.

We claim: 1. An article of. ferrous metal. havin thereon an inner coating containing tin and an outer coating of chromium.

2. Structure as set forth in claim 1 includ-,

between the "tin and chromium a coating 7 upon which bright chromium may be electro- Iyti'ca'lly deposited. 3. Structure as set forth in claim 1 includ-. 3 ing between-thetinend chmniium a, coating comprising copper I e h 4. Structure 39 set forth in claim 1 includ* mg Between the tin and chromium a. coating 'of c'opper and another of nickel. i m In testimony "whereof we afiix our signa-.

tures.

RALPH J. WIRSHING. v HENRY R. FAA S. 

